Communication Terminal Device, Base Station Device and Radio Communication System

ABSTRACT

There is disclosed a communication terminal device capable of eliminating collision of access request signals simultaneously transmitted from communication terminal devices in a local cell, preventing generation of interference signal in another cell adjacent to the local cell, and improving the throughput in the local cell. There is also disclosed a base station device for controlling the transmission power of the access permission signal so as to prevent generation of an interference signal in another cell adjacent to the local cell. In this device, a use sub-channel selection unit ( 206 ) has a correspondence table between the reception quality of the pilot signals divided into classes and the sub-channel allocated to the classes. According to the correspondence table, the use sub-channel selection unit ( 206 ) selects a sub-channel group of RACH correlated to the measurement result of the reception quality of the pilot signals reported from the reception quality measurement unit ( 205 ). One sub-channel to be used for transmission of the access request signal is selected at random from the sub-channel group selected.

TECHNICAL FIELD

The present invention relates to a radio communication system, and acommunication terminal apparatus and base station apparatus constitutingthe system.

BACKGROUND ART

Conventionally, in a radio communication system, when a communicationterminal apparatus such as a cellular telephone or the like starts radiocommunication, the communication terminal apparatus receives a pilotsignal periodically transmitted from a base station apparatus, andtransmits an access request signal subjected open-loop transmissionpower control (OL-TPC) based on reception quality of the pilot signal tothe base station apparatus using a random access channel (RACH). Then,when receiving the access request signal, the base station apparatustransmits an access permission signal to the communication terminalapparatus.

FIG. 1 schematically illustrates a configuration of a conventional radiocommunication system. The radio communication system as shown in FIG. 1is comprised of base station apparatus 11 and a plurality ofcommunication terminal apparatuses 12. Further, among the plurality ofcommunication terminal apparatuses 12, communication terminal apparatus12-1 is assumed to be positioned near base station apparatus 11 and in agood reception state. Meanwhile, communication terminal apparatus 12-2is assumed to be positioned near a boundary of a communication area bybase station apparatus 11, namely near a cell edge.

FIG. 2 illustrates radio signals on the time series transmitted andreceived between communication terminal apparatus 12 and base stationapparatus 11 when communication terminal apparatus 12 starts radiocommunication. As shown in FIG. 2, first, base station apparatus 11transmits a pilot signal with certain power to a plurality ofcommunication terminal apparatuses 12 using a common pilot channel(CPICH) on downlink.

Next, when receiving the pilot signal, communication terminal apparatus12 transmits an access request signal with transmission power associatedwith the reception quality (reception power of the pilot signal on theCPICH in FIG. 2) to base station apparatus 11 using a random accesschannel (RACH) on uplink. Resources used as a sub-channel of the RACHare predetermined such as, for example, timing, channelization code,subcarrier and the like, and communication terminal apparatus 12randomly selects one from the predetermined resources in transmittingthe access request signal.

Subsequently, when receiving the access request signal, base stationapparatus 11 transmits an access permission signal with certain power tocommunication terminal apparatus 12 using a forward access channel(FACH). Then, when receiving the access permission signal, communicationterminal apparatus 12 transmits a data packet with transmission powerassociated with the reception quality of the pilot signal to basestation apparatus 11 using a data channel on uplink. In addition, inFIG. 2, the down arrow represents downlink, while the up arrowrepresents uplink, in each channel.

Further, as well as the conventional technique as described above, atechnique is developed that communication terminal apparatus 12 firsttransmits a short packet called preamble to base station apparatus 11while increasing the transmission power gradually, and when base stationapparatus 11 detects the preamble, communication terminal apparatus 12transmits an access request signal to base station apparatus 11 (forexample, see Patent Document 1).

Patent Document 1: Japanese Patent Application Laid-Open No. 2002-528997

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, in the conventional technique as shown in FIG. 2, a pluralityof communication terminal apparatuses 12 concurrently receives the pilotsignal on the CPICH, and randomly selects sub-channels of the RACH totransmit access request signals, so that there is a risk that aplurality of communication terminal apparatuses 12 transmits accessrequest signals on the same sub-channel, and base station apparatus 11cannot receive the access request signals.

When base station apparatus 11 cannot receive an access request signalfrom communication terminal apparatus 12, base station apparatus 11 doesnot transmit an access permission signal to communication terminalapparatus 12. Therefore, communication terminal apparatus 12 determinesthat the previously transmitted access request signal is not received atbase station apparatus 11 after a predetermined time has elapsed sincetransmission of the access request signal, and transmits the accessrequest signal again to base station apparatus 11 after a lapse ofpredetermined back-off time. In other words, in such a conventionaltechnique, there is the risk that access request signals transmittedfrom a plurality of communication terminal apparatuses 12 using the RACHare not received at base station apparatus 11 due to collision, the timeis required at communication terminal apparatus 12 to determine whetherthe previously transmitted access request signal is received at basestation apparatus 11, the predetermined back-off time is further setbefore communication terminal apparatus 12 retransmits the accessrequest signal, and a problem arises that the time increases which isrequired at communication terminal apparatus 12 to start radiocommunication, and that throughput degrades in the radio communicationsystem.

Further, in the conventional technique, communication terminal apparatus12-2 positioned near the cell edge transmits the access request signalwith high power over a plurality of times, so that a problem arises thatthe access request signal becomes an interfering signal in adjacentother cells.

Furthermore, in the conventional technique, when receiving an accessrequest signal, base station apparatus 11 cannot confirm the position ofcommunication terminal apparatus 12 transmitting the access requestsignal, and base station apparatus 11 transmits an access permissionsignal with a large amount of power to be transmitted using the FACHwithout performing transmission power control so that all communicationterminal apparatuses 12 located in the cell can receive the accesspermission signal, and a problem thereby arises that the accesspermission signal becomes an interfering signal in adjacent other cellsin the same way as described above.

In the technique as disclosed in Patent Document 1, communicationterminal apparatus 12 transmits the access request signal with requiredsufficient power obtained by using the preamble to base stationapparatus 11, so that the problem is thus improved that the accessrequest signal transmitted from communication terminal apparatus 12-2located near the cell edge becomes an interfering signal in adjacentother cells. However, any improvements are not obtained in the problemthat the throughput deteriorates due to the occurrence of collision ofthe access request signals, and in the problem that the accesspermission signal transmitted from base station apparatus 11 becomes aninterfering signal in adjacent other cells.

It is therefore an object of the invention to provide a communicationterminal apparatus which avoids collision of access request signals evenwhen the access request signals are transmitted concurrently from aplurality of communication terminal apparatuses in a cell of theapparatus, prevents the occurrence of an interfering signal in othercells adjacent to the cell, and improves throughput in the cell, and abase station apparatus which controls transmission power of an accesspermission signal, and prevents the occurrence of an interfering signalin other cells adjacent to a cell of the base station apparatus.

Means for Solving the Problem

A communication terminal apparatus according to the present invention isa communication terminal apparatus which performs radio communicationwith a base station apparatus, and adopts a configuration provided witha receiving section that receives a pilot signal transmitted from thebase station apparatus, a measuring section that measures receptionquality of the received pilot signal, a selecting section that selects asub-channel to be used in transmitting a signal to the base stationapparatus according to a measurement result of the reception quality ofthe pilot signal, and a transmitting section that transmits the signalto the base station apparatus using the selected sub-channel.

ADVANTAGEOUS EFFECT OF THE INVENTION

According to the invention, even when access request signals aretransmitted concurrently from a plurality of communication terminalapparatuses in a cell of the apparatuses, it is possible to avoidcollision of the signals, prevent the occurrence of an interferingsignal in other cells adjacent to the cell, improve throughput in thecell, and further prevent the occurrence of an interfering signal inother cells adjacent to the cell by controlling transmission power of anaccess permission signal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically illustrating a configuration of aradio communication system according to conventional technique;

FIG. 2 is a diagram illustrating radio signals on the time seriestransmitted and received between a communication terminal apparatus andbase station apparatus when the communication terminal apparatus startscommunication according to the conventional technique;

FIG. 3 is a diagram schematically illustrating a configuration of aradio communication system according to Embodiment 1 of the presentinvention;

FIG. 4 is a block diagram illustrating a configuration of acommunication terminal apparatus according to Embodiment 1 of thepresent invention;

FIG. 5 is a block diagram illustrating a configuration of a base stationapparatus according to Embodiment 1 of the present invention;

FIG. 6 is a diagram illustrating an example of an assignment mode ofsub-channels of RACH to each group divided by reception quality of apilot signal when channelization codes are used as the sub-channels ofthe RACH in Embodiment 1 of the present invention;

FIG. 7 is a diagram illustrating another example of the assignment modeof sub-channels of RACH to each group divided by reception quality ofthe pilot signal when subcarriers in a multicarrier signal are used asthe sub-channels of the RACH in Embodiment 1 of the present invention;

FIG. 8 is a diagram illustrating still another example of the assignmentmode of sub-channels of RACH to each group divided by reception qualityof the pilot signal when symbols of an OFDM signal are used as thesub-channels of the RACH in Embodiment 1 of the present invention;

FIG. 9 is a diagram illustrating a correspondence between each group ofdivided communication terminal apparatuses and reception quality of thepilot signal in Embodiment 1 of the present invention;

FIG. 10 is a diagram illustrating a correspondence between each group ofdivided communication terminal apparatuses and transmission power of anaccess permission signal in Embodiment 1 of the present invention;

FIG. 11 is a diagram illustrating radio signals on the time seriestransmitted and received between the communication terminal apparatusand base station apparatus when the communication terminal apparatusstarts communication in Embodiment 1 of the present invention;

FIG. 12 is another diagram illustrating radio signals on the time seriestransmitted and received between the communication terminal apparatusand base station apparatus when the communication terminal apparatusstarts communication in Embodiment 1 of the present invention;

FIG. 13 is still another diagram illustrating radio signals on the timeseries transmitted and received between the communication terminalapparatus and base station apparatus when the communication terminalapparatus starts communication in Embodiment 1 of the present invention;

FIG. 14 is a block diagram illustrating a configuration of a basestation apparatus according to Embodiment 2 of the present invention;and

FIG. 15 is a diagram illustrating a correspondence between each group ofdivided communication terminal apparatuses and a set of a modulationscheme and coding rate in Embodiment 2 of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention will now be described below in detail withreference to accompanying drawings as appropriate. In addition, in theembodiments, components with the same function are assigned the samereference numerals, and descriptions thereof will be omitted.

Embodiment 1

FIG. 3 schematically illustrates a configuration of a radiocommunication system according to Embodiment 1 of the present invention.The radio communication system according to this embodiment is comprisedof a plurality of communication terminal apparatuses 200 and basestation apparatus 300. In the radio communication system, the pluralityof communication terminal apparatuses 200 is classified into threegroups based on reception quality of a pilot signal transmitted frombase station apparatus 300 on CPICH, for example. Hereinafter, thegroups are referred to as group 1, group 2 and group 3, in descendingorder of the reception quality. Further, communication terminalapparatuses belonging to group 1 are described as communication terminalapparatuses 200-1, communication terminal apparatuses belonging to group2 are described as communication terminal apparatuses 200-2, andcommunication terminal apparatuses belonging to group 3 are described ascommunication terminal apparatuses 200-3. Accordingly, communicationterminal apparatuses 200 existing near a cell edge belong to group 3 inthe radio communication system.

FIG. 4 is a block diagram illustrating a configuration of communicationterminal apparatus 200 according to Embodiment 1 of the invention.Communication terminal apparatus 200 has reception radio section 201,channel dividing section 202, demodulation section 203, decoding section204, reception quality measuring section 205, used sub-channel selectingsection 206, coding section 207, modulation section 208, sub-channelassigning section 209, transmission power control section 211,transmission radio section 212 and antenna element 213.

Reception radio section 201 receives a pilot signal transmitted on CPICHvia antenna element 213, access permission signal transmitted on FACHand the like from base station apparatus 300 described later, performspredetermined reception processing such as frequency conversion,analog/digital conversion and the like on the received signals, andinputs the received signals subjected to the reception processing tochannel dividing section 202.

Channel dividing section 202 determines a channel used in the receivedsignals input from reception radio section 201, and when the determinedchannel is the CPICH, inputs the received signal, namely pilot signal toreception quality measuring section 205. Meanwhile, when the determinedchannel is other than the CPICH namely FACH and the like, channeldividing section 202 inputs the received signal to demodulation section203.

Demodulation section 203 demodulates the received signal input fromchannel dividing section 202 with a predetermined scheme, and inputs thedemodulated received signal to decoding section 204.

Decoding section 204 decodes the received signal input from demodulationsection 203 with a predetermined scheme to generate reception data, andinputs the generated reception data to a control section and the likenot shown.

Reception quality measuring section 205 measures reception quality ofthe pilot signal input from channel dividing section 202, for example,Signal-to-Interference power Ratio (SIR), or a reception power level,and reports the measurement result to used sub-channel selecting section206 and transmission power control section 211.

Used sub-channel selecting section 206 has a “correspondence table”between classified reception quality of the pilot signal and sub-channelassigned to each class. Then, based on the correspondence table, usedsub-channel selecting section 206 selects a sub-channel group of theRACH associated with the measurement result of the reception quality ofthe pilot signal reported from reception quality measuring section 205,and randomly selects a single sub-channel for use in transmission of anaccess request signal from among the selected sub-channel group. Usedsub-channel selecting section 206 reports the selected sub-channel tosub-channel assigning section 209. In addition, the correspondence tablewill be described later where the classified reception quality of thepilot signal and sub-channel of the RACH assigned to each class areindicated.

Coding section 207 codes transmission data input from the controlsection and the like not shown with a predetermined scheme to generate atransmission signal, and inputs the generated transmission signal tomodulation section 208.

Modulation section 208 modulates the transmission signal input fromcoding section 207 with a predetermined scheme, and inputs the modulatedtransmission signal to sub-channel assigning section 209.

In starting radio communication, sub-channel assigning section 209assigns a predetermined resource to an access request signal input fromthe control section and the like not shown so as to transmit the accessrequest signal on the sub-channel of the RACH reported from usedsub-channel selecting section 206. Examples of the predeterminedresource include timing, channelization codes, subcarriers in amulticarrier signal and the like. Then, sub-channel assigning section209 inputs the access request signal assigned the predetermined resourceto transmission power control section 211 at predetermined timing.Further, when an access permission signal is not transmitted from basestation apparatus 300 within a predetermined time after inputting theaccess request signal to transmission power control section 211,sub-channel assigning section 209 assigns again the sub-channel of theRACH reported from used sub-channel selecting section 206 to the accessrequest signal after a lapse of predetermined back-off time, and inputsthe assigned access request signal to transmission power control section211. Meanwhile, when an access permission signal is transmitted frombase station apparatus 300 within a predetermined time after inputtingthe access request signal to transmission power control section 211,sub-channel assigning section 209 assigns a predetermined resource tothe transmission signal input from modulation section 208 so as totransmit the transmission signal on a data channel designated by theaccess permission signal, and inputs the transmission signal totransmission power control section 211 at predetermined timing.

Transmission power control section 211 amplifies the access requestsignal or transmission signal input from sub-channel assigning section209 to provide power associated with the measurement result of thereception quality of the pilot signal reported from reception qualitymeasuring section 205, and inputs the amplified access request signal ortransmission signal to transmission radio section 212.

Transmission radio section 212 performs predetermined transmissionprocessing such as digital/analog conversion, frequency conversion andthe like on the access request signal or transmission signal input fromtransmission power control section 211, and wirelessly transmits thesignal to base station apparatus 300 via antenna element 213.

FIG. 5 is a block diagram illustrating a configuration of base stationapparatus 300 according to Embodiment 1 of the invention. Base stationapparatus 300 has reception radio section 301, RACH detecting section302, demodulation section 303, decoding section 304, requiredtransmission power calculating section 305, coding section 306,modulation section 307, transmission power control section 308,multiplexing section 309, transmission radio section 311 and antennaelement 312.

Reception radio section 301 receives the access request signaltransmitted on the RACH and transmission signal transmitted on the datachannel from communication terminal apparatus 200 via antenna element312, performs predetermined reception processing such as frequencyconversion, analog/digital conversion and the like on the receivedsignals, and inputs the received signals subjected to the receptionprocessing to RACH detecting section 302.

RACH detecting section 302 detects the access request signal from thereceived signals input from reception radio section 301, and when theaccess request signal is detected, inputs the access request signal torequired transmission power calculating section 305. Meanwhile, when theaccess request signal is not detected, RACH detecting section 302determines that the received signals include only normal data signals,and inputs the received signals to demodulation section 303.

Demodulation section 303 performs demodulation processing on thereceived signal input from RACH detecting section 302 with apredetermined scheme, and inputs the demodulated received signal todecoding section 304.

Decoding section 304 decodes the received signal input from demodulationsection 303 with a predetermined scheme to generate reception data, andinputs the generated reception data to a control section and the likenot shown.

Required transmission power calculating section 305 determines thesub-channel of the RACH used in transmission of the access requestsignal input from RACH detecting section 302. Required transmissionpower calculating section 305 has the correspondence table that usedsub-channel selecting section 206 has, and based on the correspondencetable, required transmission power calculating section 305 recognizesthe reception quality of the pilot signal in communication terminalapparatus 200 from the determined RACH sub-channel. Further, requiredtransmission power calculating section 305 also has a “conversion table”that associates the determined sub-channel with transmission power ofthe access permission signal, calculates the transmission powerassociated with the determined RACH sub-channel using the conversiontable, and reports the calculated transmission power to transmissionpower control section 308. In addition, the conversion table will bedescribed later.

Coding section 306 performs coding processing on the access permissionsignal or transmission data input from the control section and the likenot shown with a predetermined scheme to generate a transmission signal,and inputs the generated transmission signal to modulation section 307.

Modulation section 307 modulates the transmission signal input fromcoding section 306 with a predetermined scheme, and inputs the modulatedtransmission signal to transmission power control section 308.

Transmission power control section 308 amplifies the transmission signalinput from modulation section 307 to provide power reported fromrequired transmission power calculating section 305, and inputs theamplified transmission signal to multiplexing section 309.

Multiplexing section 309 receives a pilot signal from the controlsection and the like not shown periodically, multiplexes the pilotsignal on the transmission signal input from transmission power controlsection 308 at timing at which the pilot signal is input, and inputs themultiplexed transmission signal to transmission radio section 311. Inaddition, multiplexing section 309 causes the transmission signal inputfrom transmission power control section 308 to pass through transmissionradio section 311 without change at timing at which the pilot signal isnot input.

Transmission radio section 311 performs transmission processing such asdigital/analog conversion, frequency conversion and the like on thetransmission signal input from multiplexing section 309, and wirelesslytransmits the transmission signal subjected to the transmissionprocessing to communication terminal apparatus 200 via antenna element312.

The operation of communication terminal apparatus 200 and base stationapparatus 300 will be described below in detail with reference to FIG. 6to FIG. 13.

FIG. 6 shows an assignment mode of channelization codes to group 1,group 2 and group 3 classified based on the reception quality of thepilot signal when communication terminal apparatus 200 uses thechannelization code as a resource of the sub-channel of the RACH. InFIG. 6, two channelization codes #1 and #2 are assigned to group 1 withthe highest reception quality of the pilot signal, three channelizationcodes #3, #4 and #5 are assigned to group 2 with the middle receptionquality, and all of remaining usable channelization codes #6 to #n (n isa natural number of ten or more), are assigned to group 3 with thelowest reception quality.

Further, FIG. 7 shows an assignment mode of subcarriers to group 1,group 2 and group 3 classified based on the reception quality of thepilot signal when communication terminal apparatus 200 uses thesubcarriers in a multicarrier signal as a resource of the sub-channel ofthe RACH. In FIG. 7, two subcarriers #1 and #2 are assigned to group 1with the highest reception quality of the pilot signal, threesubcarriers #3, #4 and #5 are assigned to group 2 with the middlereception quality, and all of remaining usable subcarriers #6 to #n (nis a natural number of ten or more) are assigned to group 3 with thelowest reception quality.

Furthermore, FIG. 8 shows an assignment mode of symbols of an OFDM(Orthogonal Frequency Division Multiplexing) signal to group 1, group 2and group 3 classified based on the reception quality of the pilotsignal when communication terminal apparatus 200 uses the symbols in anOFDM signal as a resource of the sub-channel of the RACH. In FIG. 8,first two symbols of an OFDM signal are assigned to group 1 with thehighest reception quality of the pilot signal, subsequent three symbolsof the OFDM signal are assigned to group 2 with the middle receptionquality, and all of remaining usable symbols of the OFDM signal areassigned to group 3 with the lowest reception quality. In addition, alsowhen the resource of the sub-channel of the RACH is a time slotstandardized in a communication scheme, the time slot can be assigned asin the symbol of an OFDM signal.

FIG. 9 shows an example of the correspondence table provided in usedsub-channel selecting section 206. In the correspondence table, group 1is of the case that the measurement result of reception SIR is 15 dB ormore as the reception quality of the pilot signal by reception qualitymeasuring section 205, group 2 is of the case that the measurementresult is 5 to 15 dB, and group 3 is of the case that the measurementresult is −3 to 5 dB. Group 1, group 2 and group 3 as shown in FIG. 9are respectively assigned sub-channels in modes as shown in FIG. 6 toFIG. 8. Accordingly, based on the correspondence table, used sub-channelselecting section 206 selects sub-channels of the RACH assigned in themodes as shown in FIGS. 6 to 8 corresponding to the measurement resultof the reception quality of the pilot signal reported from receptionquality measuring section 205, and randomly selects one sub-channel tobe used in transmitting the access request signal from among theselected plurality of sub-channels. In addition, any groups are notassociated with the case that the measurement result is less than −3 dBin the reception quality of the pilot signal by reception qualitymeasuring section 205. This is because when the measurement result ofthe reception quality of the pilot signal is less than −3 dB, thepropagation path condition is excessively poor, and the risk is therebyhigh that base station apparatus 300 does not receive an access requestsignal even when communication terminal apparatus 200 transmits theaccess request signal. Therefore, in order to prevent the occurrence ofan interfering signal in adjacent other cells, communication terminalapparatus 200 is prevented from transmitting an unnecessary accessrequest signal. In addition, in this case, when communication terminalapparatus 200 recovers from the attenuation due to fading, shadowing orthe like on the propagation path and has the measurement result of −3 dBor more in the reception quality of the pilot signal, communicationterminal apparatus 200 can access base station apparatus 300.

FIG. 10 shows an example of the conversion table that requiredtransmission power calculating section 305 has. The conversion table hasa correlation with the correspondence table as shown in FIG. 9. On theassumption that the required reception SIR is 0 dB for the accesspermission signal in communication terminal apparatus 200, thetransmission power of the access permission signal in base stationapparatus 300 is expressed by decibel based on the transmission power ofthe pilot signal. More specifically, for group 1, since the measurementresult is 15 dB or more in the reception quality of the pilot signal incommunication terminal 200-1, in order that the reception quality is 0dB or more in the access permission signal in communication terminalapparatus 200-1, the transmission power of the access permission signalin base station apparatus 300 is set at −15 dB based on the transmissionpower of the pilot signal. Similarly, for group 2, since the measurementresult is 5 dB or more in the reception quality of the pilot signal incommunication terminal 200-2, the transmission power of the accesspermission signal in base station apparatus 300 is set at −5 dB based onthe transmission power of the pilot signal. Further, for group 3, sincethe measurement result is −3 dB or more in the reception quality of thepilot signal in communication terminal 200-3, the transmission power ofthe access permission signal in base station apparatus 300 is set at 3dB based on the transmission power of the pilot signal.

FIG. 11 illustrates radio signals on the time series transmitted andreceived between communication terminal apparatus 200-1 belonging togroup 1 and base station apparatus 300 when communication terminalapparatus 200-1 starts communication. Similarly, FIG. 12 illustratesradio signals on the time series transmitted and received betweencommunication terminal apparatus 200-2 belonging to group 2 and basestation apparatus 300 when communication terminal apparatus 200-2 startscommunication. Further, FIG. 13 illustrates radio signals on the timeseries transmitted and received between communication terminal apparatus200-3 belonging to group 3 and base station apparatus 300 whencommunication terminal apparatus 200-3 starts communication. Inaddition, in FIG. 11 to FIG. 13, a reception power level of a pilotsignal is used as the reception quality of the pilot signal. As shown inFIG. 11 to FIG. 13, based on the measurement result of the receptionquality of the pilot signal, communication terminal apparatuses 200-1 to200-3 perform transmission power control on the access request signaltransmitted on the RACH and a data packet transmitted on the datachannel. Meanwhile, base station apparatus 300 determines thesub-channel of the RACH used by communication terminal apparatus 200,indirectly recognizes the measurement result of the reception quality ofthe pilot signal in communication terminal apparatus 200, namelyrecognizes that communication terminal apparatus 200 belongs to whichgroup among groups 1 to 3, and performs transmission power control onthe access permission signal transmitted on the FACH. Accordingly, bycomparing between FIG. 11 and FIG. 13, it is understood that thetransmission power on the FACH to transmit the access permission signalis different from one another, and that the transmission power on theFACH is the highest in FIG. 13 showing communication terminal apparatus200-3 with the lowest reception quality of the pilot signal.

Thus, according to the radio communication system according to thisEmbodiment, communication terminal apparatus 200 classifies measurementresults of the reception quality of the pilot signal, assigns dedicatedRACH sub-channels to each class beforehand, and selects an RACHsub-channel to use in transmitting an access request signal according toan actual measurement result, so that it is possible to decrease theprobability that a plurality of communication terminal apparatuses 200concurrently uses the same RACH sub-channel. As a result, according tothe radio communication system according to this embodiment, the accessrequest signal is received reliably in base station apparatus 300, thenumber of retransmissions of the access request signal decreases, sothat it is possible for communication terminal apparatus 200 to startradio communication in a short period, improve throughput in the cell,and prevent the occurrence of an interfering signal in other cellsadjacent to the cell.

Further, according to the radio communication system according to thisembodiment, base station apparatus 300 transmits the access permissionsignal with required sufficient transmission power according to thereception quality of the access request signal in each of communicationterminal apparatuses 200-1 to 200-3, so that it is possible to preventthe access permission signal from being an interfering signal in othercells adjacent to the cell of base station apparatus 300.

Furthermore, according to the radio communication system according tothis embodiment, in the correspondence table provided in usedsub-channel selecting section 206 in communication terminal apparatus200, a larger number of sub-channels are assigned to a lower class (forexample, group 3) than a higher class (for example, group 1) inclassified reception quality of the pilot signal. By this means,communication terminal apparatuses 200 positioned nearer the cell edgedecrease the probability of concurrently using the same RACHsub-channel, and the number of retransmissions of the access requestsignal decreases that it is possible to efficiently prevent theoccurrence of the interfering signal in other cells adjacent to the cellof communication terminal apparatuses 200.

Moreover, in the radio communication system according to thisembodiment, in the correspondence table provided in used sub-channelselecting section 206 at communication terminal apparatus 200, withrespect to the classified reception quality of the pilot signal, a rangeof the reception quality in a lower class is narrower than that in ahigher class. More specifically, the range of the reception quality ofgroup 1 is 15 dB or more without an upper limit, the range of thereception quality of group 2 is 10 dB of between 5 and 15 dB, and therange of the reception quality of group 3 is 8 dB of between −3 and 5dB. Therefore, according to the radio communication system according tothis embodiment, since a larger number of sub-channels are assigned to alower class with a narrower range of the reception quality of the pilotsignal, it is possible to further reduce efficiently the number ofretransmissions of the access request signal of communication terminalapparatus 200 positioned near the cell edge, so that it is possible toprevent the occurrence of the interfering signal in other cells adjacentto the cell of communication terminal apparatus 200 more effectively.

In addition, this embodiment may be modified and applied as describedbelow.

In base station apparatus 300 according to this embodiment, the case hasbeen described where required transmission power calculating section 305determines a sub-channel of the RACH used in transmission of the accessrequest signal, and reports transmission power control section 308 oftransmission power associated with the determined sub-channel, but theinvention is not limited to this case. For example, requiredtransmission power calculating section 305 may have a request signalmeasuring section that measures reception quality of an access requestsignal, compare the reception quality measured in the request signalmeasuring section with required reception quality in communicationterminal apparatus 200, namely target reception quality in transmissionpower control, increase or decrease the transmission power associatedwith the sub-channel of the RACH when a difference of the receptionquality is larger than a predetermined value, and report the increasedor decreased transmission power to transmission power control section308.

Calculation of the transmission power of the access permission signal inrequired transmission power calculating section 305 is calculation byclosed-loop based on the reception quality of the access request signalTherefore, when the time is required at communication terminal apparatus200 from the reception of a pilot signal until the transmission of anaccess request signal or when the variation is intense in propagationpath conditions, there is a risk that actual propagation path conditionsare not reflected in the calculated transmission power. Then, ifrequired transmission power calculating section 305 performs calculationof the transmission power by open-loop for measuring the receptionquality of the access request signal, in addition to calculation of thetransmission power by closed-loop, it is possible to performtransmission power control of the access permission signal moreaccurately.

Embodiment 2

Embodiment 2 of the invention describes the case where a base stationapparatus varies adaptively a coding rate and modulation scheme on theFACH based on used resources of the RACH. In addition, a configurationof a communication terminal apparatus according to this embodiment isthe same as that in FIG. 4, and described using FIG. 4.

FIG. 14 is a block diagram illustrating a configuration of base stationapparatus 400 according to Embodiment 2 of the invention. Base stationapparatus 400 has reception radio section 301, RACH detecting section302, demodulation section 303, decoding section 304, adaptive controlsection 413, coding section 406, modulation section 407, multiplexingsection 309, transmission radio section 311 and antenna element 312.

Adaptive control section 413 determines a sub-channel of the RACH usedin transmission of an access request signal input from RACH detectingsection 302, sets a modulation scheme and coding rate using a conversiontable that associates the determined sub-channel with a transmissionparameter, namely a set of the modulation scheme and coding rate of anaccess permission signal, and inputs the set modulation scheme andcoding rate to coding section 406 and modulation section 407.

Coding section 406 performs coding processing on the access permissionsignal or transmission data input from the control section and the likenot shown with the coding rate or coding method according to thetransmission parameter (information of the coding rate and modulationscheme) input from adaptive control section 413 to generate atransmission signal, and inputs the generated transmission signal tomodulation section 407.

Modulation section 407 modulates the transmission signal input fromcoding section 406 with the modulation scheme according to thetransmission parameter input from adaptive control section 413, andinputs the modulated transmission signal to multiplexing section 309.

FIG. 15 shows an example of the conversion table that adaptive controlsection 413 has. The conversion table has a correlation with thecorrespondence table as shown in FIG. 9, and as the reception quality incommunication terminal apparatus 200 is higher, the modulation level andcoding rate increase. For example, in group 1, since the receptionquality is 15 dB or more, the transmission parameter such that therequired SIR is 15 dB, namely 16QAM and R=¾ is used that is thetransmission parameter with the highest transmission efficiency enablingreception with a sufficiently low error rate when the reception SIR is15 dB or more. In group 2, since the reception SIR is 5 dB to 15 dB,QPSK and R=½ is used that is the transmission parameter such that thereception SIR is 5 dB. The same also applies to group 3.

As the transmission parameter has higher transmission efficiency, it ispossible for base station apparatus 400 to finish transmission of theaccess permission signal in a shorter time.

Thus, according to this embodiment, base station apparatus 400 transmitsan access permission signal using a transmission parameter with thehighest transmission efficiency that allows reception with asufficiently low error rate according to the reception quality of theaccess request signal in each of communication terminal apparatuses200-1 to 200-3, so that it is possible to reduce the transmission timeof the access permission signal, and prevent the access permissionsignal from being an interfering signal in other cells.

Each of the above-mentioned Embodiments has described the case where theinvention is constructed by hardware as an example, but it is alsopossible to implement the present invention by software.

Each function block employed in the description of each of theaforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. “LSI” is assumed herebut this may also be referred to as “IC”, “system LSI”, “super LSI”,“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand setting of circuit cells within an LSI can be reconfigured is alsopossible.

Furthermore, if integrated circuit technology comes out to replace LSI'sas a result of the advancement of semiconductor technology or aderivative other technology, it is naturally also possible to carry outfunction block integration using this technology. Application inbiotechnology is also possible.

In addition, in the radio communication system according to each of theabove-mentioned embodiments, the case has been described where aplurality of communication terminal apparatuses 200 is divided intothree groups in association with classes of the reception quality of thepilot signal, but the invention is not limited to this case. Forexample, the number of groups may be increased.

Further, the access permission signal may be transmitted, for example,in 3GPP standards, using AICH (Acknowledge Indicator Channel), FACH(Forward Access Channel), S-CCPCH (Secondary-Common Control PhysicalChannel), HS-SCCH (High Speed-Shared Control Channel), and DPCH(Dedicated Physical Channel).

Furthermore, in each of the above-mentioned embodiments, it is describedthat an access request is made on the RACH, access permission is made onthe FACH, and then, data packets are transmitted. However, the sameeffects are obtained when the RACH is used in transmission of data aswell as the access request signal, and the FACH is used in transmissionof data as well as the access permission signal. For example, for ashort packet, packet with demanding delay requirement and the like, thedata packet on uplink may be transmitted on the RACH, while the datapacket on downlink may be transmitted on the FACH.

Still furthermore, the RACH in each of the above-mentioned embodimentsmay be another comparable channel to which resource are not assignedbeforehand for each user.

Moreover, in each of the above-mentioned embodiments, it is describedthat the reception quality is estimated from the reception SIR, but thereception quality may be estimated from reception SNR, reception CIR,reception SINR, reception CINR, reception power, interfering power, biterror rate, throughput, MCS (a combination of a modulation scheme andcoding rate) capable of achieving a predetermined error rate, and thelike. Further, the base station apparatus may be represented by Node B,and the communication terminal apparatus may be represented by UE.

A first aspect of the invention is a communication terminal apparatuswhich performs radio communication with a base station apparatus, andhas a receiving section that receives a pilot signal transmitted fromthe base station apparatus, a measuring section that measures receptionquality of the received pilot signal, a selecting section that selects asub-channel to be used in transmitting a signal to the base stationapparatus according to a measurement result of the reception quality ofthe pilot signal, and a transmitting section that transmits the signalto the base station apparatus using the selected sub-channel.

A second aspect of the invention is a communication terminal apparatuswhere in the above-mentioned invention, the transmitting sectiontransmits the signal using a random access channel.

A third aspect of the invention is a communication terminal apparatuswhere in the above-mentioned invention, the transmitting sectiontransmits an access request signal.

A fourth aspect of the invention is a communication terminal apparatuswhere the selecting section assigns a larger number of sub-channels to alower class than a higher class in classified reception quality, andselects the sub-channel to be used in transmitting the signal to thebase station apparatus from among sub-channels assigned to a classcorresponding to the measurement result of the reception quality of thepilot signal.

A fifth aspect of the invention is a communication terminal apparatuswhere in the above-mentioned invention, the selecting section assignssub-channels to each class by narrowing a range of the reception qualityfor a lower class than a higher class in the classified receptionquality, and selects the sub-channel to be used in transmitting thesignal to the base station apparatus from among the sub-channelsassigned to the class corresponding to the measurement result of thereception quality of the pilot signal.

A sixth aspect of the invention is a base station apparatus whichperforms radio communication with a communication terminal apparatus,and has a receiving section that receives a signal transmitted from thecommunication terminal apparatus, a detecting section that detects asub-channel used in transmitting the received signal, and a transmittingsection that transmits the signal to the communication terminalapparatus with transmission power associated with the detectedsub-channel, or a modulation scheme and coding rate associated with thedetected sub-channel.

A seventh aspect of the invention is the base station apparatus where inthe above-mentioned invention, the transmitting section transmits anaccess permission signal.

An eighth aspect of the invention is a base station apparatus where inthe above-mentioned embodiment, a request signal measuring section isfurther provided that measures reception quality of the signal receivedby the receiving section, and the transmitting section increases ordecreases transmission power associated with the sub-channel detected inthe detecting section, according to a difference between the receptionquality measured by the request signal measuring section and targetreception quality in transmission power control, and transmits thesignal with increased or decreased power to the communication terminalapparatus.

A ninth aspect of the invention is a base station apparatus where in theabove-mentioned invention, the receiving section receives the signaltransmitted using a random access channel.

A tenth aspect of the invention is a radio communication systemcomprised of a communication terminal apparatus and a base stationapparatus, where the communication terminal apparatus has a terminalreceiving section that receives a pilot signal transmitted from the basestation apparatus, a measuring section that measures reception qualityof the received pilot signal, a selecting section that selects asub-channel to be used in transmitting a signal to the base stationapparatus according to a measurement result of the reception quality ofthe pilot signal, and a terminal transmitting section that transmits thesignal to the base station apparatus using the selected sub-channel, andthe base station apparatus has a base station receiving section thatreceives the signal transmitted from the communication terminalapparatus, a detecting section that detects the sub-channel used intransmitting the received signal, and a base station transmittingsection that transmits the signal to the communication terminalapparatus with transmission power associated with the detectedsub-channel.

An eleventh aspect of the invention is a radio communication systemwhere in the above-mentioned invention, the terminal transmittingsection transmits an access request signal.

A twelfth aspect of the invention is a radio communication system wherein the above-mentioned invention, the base station transmitting sectiontransmits an access permission signal.

The present application is based on Japanese Patent Application No.2004-173017, filed on Jun. 10, 2004, entire content of which isexpressly incorporated by reference herein.

INDUSTRIAL APPLICABILITY

The communication terminal apparatus and base station apparatusaccording to the present invention have effects of decreasing theincidence of collision of access request signals in a cell of theapparatus, preventing the occurrence of an interfering signal in othercells adjacent to the cell, and improving throughput in the cell, andare useful in a radio communication system and the like.

1. A communication terminal apparatus that performs radio communicationwith a base station apparatus, comprising: a receiving section thatreceives a pilot signal transmitted from said base station apparatus; ameasuring section that measures reception quality of said received pilotsignal; a selecting section that selects a sub-channel to be used intransmitting a signal to said base station apparatus according to ameasurement result of the reception quality of said pilot signal; and atransmitting section that transmits said signal to said base stationapparatus using the selected sub-channel.
 2. The communication terminalapparatus according to claim 1, wherein said transmitting sectiontransmits said signal using a random access channel.
 3. Thecommunication terminal apparatus according to claim 1, wherein saidtransmitting section transmits an access request signal.
 4. Thecommunication terminal apparatus according to claim 1, wherein saidselecting section assigns a larger number of sub-channels to a lowerclass than a higher class in classified reception quality, and selectsthe sub-channel to be used in transmitting the signal to said basestation apparatus from among sub-channels assigned to a classcorresponding to the measurement result of the reception quality of saidpilot signal.
 5. The communication terminal apparatus according to claim1, wherein said selecting section assigns sub-channels to each class bynarrowing a range of the reception quality for a lower class than ahigher class in the classified reception quality, and selects thesub-channel to be used in transmitting the signal to said base stationapparatus from among the sub-channels assigned to the classcorresponding to the measurement result of the reception quality of saidpilot signal.
 6. A base station apparatus that performs radiocommunication with a communication terminal apparatus, comprising: areceiving section that receives a signal transmitted from saidcommunication terminal apparatus; a detecting section that detects asub-channel used in transmitting said received signal; and atransmitting section that transmits the signal to said communicationterminal apparatus with transmission power associated with said detectedsub-channel, or a modulation scheme and coding rate associated with saiddetected sub-channel.
 7. The base station apparatus according to claim6, wherein said transmitting section transmits an access permissionsignal.
 8. The base station apparatus according to claim 6, furthercomprising a request signal measuring section that measures receptionquality of the signal received by said receiving section, wherein saidtransmitting section increases or decreases transmission powerassociated with said sub-channel detected by said detecting sectionaccording to a difference between the reception quality measured by saidrequest signal measuring section and target reception quality intransmission power control, and transmits the signal with increased ordecreased power to said communication terminal apparatus.
 9. The basestation apparatus according to claim 6, wherein said receiving sectionreceives the signal transmitted using a random access channel.
 10. Aradio communication system comprised of a communication terminalapparatus and a base station apparatus, wherein: said communicationterminal apparatus comprises a terminal receiving section that receivesa pilot signal transmitted from said base station apparatus, a measuringsection that measures reception quality of said received pilot signal, aselecting section that selects a sub-channel to be used in transmittinga signal to said base station apparatus according to a measurementresult of the reception quality of said pilot signal, and a terminaltransmitting section that transmits said signal to said base stationapparatus using the selected sub-channel; and said base stationapparatus comprises a base station receiving section that receives saidsignal transmitted from said communication terminal apparatus, adetecting section that detects the sub-channel used in transmitting saidreceived signal, and a base station transmitting section that transmitsthe signal to said communication terminal apparatus with transmissionpower associated with said detected sub-channel.
 11. The radiocommunication system according to claim 10, wherein said terminaltransmitting section transmits an access request signal.
 12. The radiocommunication system according to claim 10, wherein said base stationtransmitting section transmits an access permission signal.